Optical recording materials comprising antimony-tin alloys including a third element

ABSTRACT

Antimony-tin alloys including a third element are useful for phase change optical recording. Some preferred alloys have a higher amorphous to crystalline transition temperature and thus, amorphous areas are stable for longer periods. Other preferred alloys exhibit improved CNR or lower noise or other improved performance characteristics.

This is a divisional of application Ser. No. 229,958, filed Aug. 9, 1988now abandoned.

FIELD OF THE INVENTION

This invention relates to antimony-tin alloys that are useful in opticalrecording.

CROSS REFERENCE TO RELATED APPLICATIONS

The following commonly assigned, copending applications, each entitledRECORDING ELEMENT COMPRISING WRITE-ONCE THIN FILM ALLOY LAYERS, discloseand claim related inventions:

U.S. Ser. No. 014,336 filed Feb. 13, 1987 by Pan, Tyan and Preuss, nowabandoned in favor of CIP U.S. Ser. No. 194,605 filed May 16, 1988;(antimony-tin and antimony-tin and indium);

U.S. Ser. No. 014,337 filed Feb. 13, 1987 by Pan, Tyan and Marino; anddivisional U.S. Ser. No. 197,557 filed May 23, 1988; (antimony-tin andgermanium);

U.S. Ser. No. 058,721 filed June 5, 1987 by Pan, Tyan and Vazan;(antimony-tin and aluminum);

U.S. Ser. No. 058,722 filed June 5, 1987 by Pan, Tyan and Preuss;(antimony-tin and zinc).

BACKGROUND OF THE INVENTION

Thin film optical recording layers using chalcogenide thin films andamorphous to crystalline phase transitions have been the subject of manyinvestigations since the early 1970's. The initial interests werefocused on "erasable", and therefore reusable, optical recording layerssince the amorphous to crystalline transition is, in principle, areversible process. A low power, relatively long duration laser pulse isused to heat a local spot on the layer to below the melting point for asufficient length of time to cause the spots to crystallize. Thesecrystalline spots can in turn be heated, by a higher power, shorterduration laser, above the melting point of the crystallized spots torandomize the structure of the spots. The layer is designed such thatupon the termination of the laser pulse, the cooling rate of the heatedspot is high enough that the randomized structure is frozen to achievean amorphous state.

Thus, by adjusting the laser power and duration, the state of a selectedarea on the layer can be switched between the amorphous state and thecrystalline state to create a pattern of amorphous and crystalline spotswhich can be used for information storage. Since the phase transition isreversible, &he pattern can be erased and replaced with a differentrecorded pattern. Theoretically, this erase write cycle can be carriedout any number of times.

Very few materials are known for optical recording layers in which theabove described write-erase-write cycle is of practical use. No erasablephase-change type optical recording layers have been commercialized.

European Patent Application No. 0184452 discloses certain erasableoptical recording layers of antimony indium and antimony-indium-tinalloys. Information recording and erasure are said to be achieved byswitching the layers between two different crystalline states. Thelayers are generally prepared in the amorphous state which has to befirst converted into one of the two crystalline states beforeinformation can be recorded. The crystallized states, achieved by eithera bulk heat-treatment or a prolonged laser exposure, are said to have alower reflectance than the amorphous state. The examples indicate thatthe materials disclosed therein have a very slow rate ofcrystallization. This application further teaches that the opticalrecording layers disclosed therein are unsuitable for use in theamorphous-to-crystalline transition mechanism because of the instabilityof the amorphous state in general. Thus, because of the slow amorphousto crystalline transition and the instability of the amorphous state,the alloys disclosed in this reference are not suited to write-oncerecording.

A good deal of attention has also focused on so-called "write once" thinfilm optical recording layers. Write-once simply means that the layerscan be recorded upon only once. Such layers cannot be erased and reusedfor a subsequent recording.

Since thin film optical recording layers are generally amorphous whenprepared, it is desirable to use the crystallization step as therecording step in write-once layers. However, the problem of slowcrystallization prevents the achievement of high data rates with mostknown materials. High data rates are critical for write-once layersdesigned for use with computers.

Thus, a principal difficulty is that the rate of crystallization of mostlayers studied is usually too low. For practical applications, it isdesirable to have layers which can be crystallized by laser pulsesshorter than a microsecond (μs). Presently, few materials havedemonstrated such capabilities. For some materials that do have highcrystallization rates (e.g. Te-Sn alloys, the data retention times areoften not adequate because of the instability of the amorphous state.

Thus, the problem was that the prior art had not provided write-onceoptical recording layers which possess the combination of (a) acrystallization rate less than 1.0 μs, (b) good corrosion resistance,(c) a stable amorphous state and (d) a capability of high rate, highdensity recordings.

This problem was solved in the first mentioned related application;copending U.S. Ser. No. 014,336 filed 2/13/87. In that application thereis disclosed an alloy of antimony-tin and, in preferred embodiments, athird element indium, which alloy is capable of high performancewrite-once optical recording. The recording materials of thatapplication do not suffer the environmental corrosion seen in chalcogenrich thin films typically used for write-once applications. The rate ofcrystallization of the antimony-tin optical recording layers is lessthan 1 μs using practical laser power (<12 mW). The dynamic recordingsensitivity at 10 m/s is in the range of 3.5 to 6.5 mW. The amorphousstate is very stable, particularly in those embodiments where the alloyincludes indium. Thus, recordings on the thin film are made using theamorphous to crystalline transition mechanism. The layers are capable ofhigh density, high rate recordings having a dynamic carrier-to-noiseratio (CNR) over 55 decibels, particularly in the range of 60 to 65decibels.

The superior properties of these alloys are believed to be a result ofthe NaCl (or slightly distorted NaCl) type crystalline structure of theantimony-tin intermetallic phase. It is believed that this structurefacilitates the fast transformation from the amorphous phase. While thebinary antimony-tin alloy performs better than prior art materials, itstill has a relatively low crystallization temperature and hence, is notsuitable for applications where severe temperature conditions are to beexpected. Further, the carrier to noise ratio is about 55 dB for thebinary alloy. This is adequate for most applications but improvement isdesirable for more demanding ones.

Indium can be used to stabilize the amorphous phase by increasing theamorphous to crystalline transition temperature. Indium was firstselected since its atomic number (49) is similar to that of antimony(51) and tin (50). The use of indium also results in a significantimprovement in the carrier-to-noise ratio of the recording process.

Subsequent to the discovery that indium could be used to improve theproperties of the basic antimony-tin alloy, other basically antimony-tinalloys were discovered by the present assignee. Thus, applications werefiled on antimony-tin alloys containing aluminum (U.S. Ser. No. 058,721filed June 5, 1987); zinc (U.S. Ser. No. 058,722 filed June 6, 1987);and germanium (U.S. Ser. No. 014,337 filed Feb. 13, 1987).

In Japanese published patent application number J62-246,788, publishedOct. 27, 1987 there is disclosed an antimony-tin-germanium alloy foroptical recording. There is no suggestion in this publication that anyother third element could be used with antimony-tin.

A number of other publications disclose a variety of alloys that areproposed for optical recording. However, none of these publicationsspecifically disclose antimony-tin alloys of the present type, that is,alloys that have the advantageous combination of properties describedabove. Representative references are: U.S. Pat. No. 4,686,543 to Tani etal; U.S. Pat. No. 4,405,706 to Takahashi et al; 4,357,616 to Terao etal; 4,230,939 to deBont et al; 4,647,944 to Gravesteijn; and Japanesepublished applications numbers J60-177,446 and J58-7,394.

SUMMARY OF THE INVENTION

In accordance with the present invention, it has now been found that theelement that is used in the antimony-tin recording alloy does not haveto be indium, aluminum, zinc or germanium. Other elements can be used inthe alloy to improve the amorphous to crystalline transitiontemperature, the carrier to noise ratio or other property of therecording layer. Thus, in accordance with the present invention there isprovided a recording material comprising a write-once amorphous thinfilm optical recording layer of an alloy, said alloy comprising (1)antimony and tin in an amount and a proportion such that crystallinelaser recorded marks of said alloy have a sodium chloride or a slightlydistorted sodium chloride type crystal and (2) at least one otherelement, provided that said other element is not indium, aluminum, zincor germanium.

In preferred embodiments, the additional element present in the alloycauses the amorphous to crystalline transition temperature to increase.The increase in the amorphous to crystalline transition temperature isimportant for the long term stability of the recording material.Recording layers having a higher transition temperature will be lessprone to spontaneous amorphous to crystalline transition. It isestimated for example, (assuming 100 Kcal/mole activation energy, 50° C.storage temperature and that a 0.1% crystallization results in recordinglayer failure) that an alloy having a transition temperature of about90° C. will have a storage lifetime of about 1 year. If the transitiontemperature is increased to about 110° C., the storage lifetime will beincreased to about 1500 years.

Elements which have been found to increase the amorphous to crystallinetransition temperature include, in addition to indium, aluminum, zincand germanium, cadmium, nickel, iron, manganese, copper, oxygen, niobiumand silicon. Thus, these are preferred elements for the antimony-tinalloys.

In other preferred embodiments, the recording materials of the inventionwill exhibit improved carrier-to-noise ratio when the recording materialis used for optical recording. It appears that the additional element inthe alloy makes the layer of the alloy smoother or makes the alloyharder so that there is less deformation when a laser is used to makethe crystalline marks.

Elements which have been found to increase the carrier to noise ratio ofrecorded layers include, in addition to indium, chromium, bismuth,niobium and tungsten. Thus, these elements are al so preferred in thepresent invention.

As with the antimony-tin (binary) and antimony-tin-indium alloys, thecrystalline areas that are produced by laser recording are all in thesame crystalline state and are thus distinguishable from the typicalerasable recorded layers as illustrated by the materials described inEuropean Patent Application No. 0184452 mentioned above.

Thus, in another aspect of the invention there is provided a recordedmaterial comprising an amorphous thin film optical recording layer of analloy having information recorded wherein in the form of crystallineareas in said layer, the crystalline areas all being the samecrystalline state, said alloy comprising (1) antimony and tin in anamount and a proportion such that said crystalline areas have a sodiumchloride or a distorted sodium chloride type crystal and (2) at leastone other element, provided that said other element is not indium,aluminum, zinc or germanium.

In still another aspect of the invention, there is provided a method ofrecording information, comprising the steps of:

(a) providing a recording material comprising a write-once amorphousthin-film optical recording layer of an alloy, said alloy comprising (1)antimony and tin in an amount and a proportion such that crystallinelaser recorded marks of said alloy have a sodium chloride or a distortedsodium chloride type crystal and (2) at least one other element,provided that said other element is not indium, aluminum, zinc orgermanium,

(b) focusing an information modulated laser beam on said recording layerto form a pattern of crystalline and amorphous areas in the layer;wherein all of said crystalline areas are in the same crystalline statewith a reflectivity that is different from the amorphous areas.

It was surprising that an alloy could be found for write-onceapplication, that had a combination of (a) a crystallization rate lessthan 1.0 μs, (b) good corrosion resistance, (c) a stable amorphous stateand (d) a capability of high rate, high density recordings, and retainedthis combination of properties even where an additional element wasincluded in the alloy. The concern was that the additional element coulddisrupt the crystal structure of the crystalline phase and thereforereduce or eliminate the useful performance of the basic antimony-tinalloy. It was particularly surprising that in some cases, theperformance was actually increased.

DETAILED DESCRIPTION OF THE INVENTION

As we have now found, the selection of the additional element that isadded to the antimony-tin alloy is not critical. In addition to indium,aluminum, zinc and germanium which are the subject of the relatedapplications mentioned above, cadmium, gallium, titanium, silicon,manganese, tellurium, niobium, iron, copper, tungsten, lead, molybdenum,sulfur, nickel, oxygen, selenium, thallium, arsenic, phosphorous, gold,palladium, platinum, hafnium and vanadium can be used. Mixtures of theseelements are also useful.

The amount of the third element to be included in the alloy will dependon the element selected and the property to be improved. For example,the amount can range from the minimum amount that noticeably improvescarrier-to-noise ratio when the alloy is used for recording up to theamount that the performance of the write-once antimony-tin propertiesare degraded, that is, up to the point where the element begins tointerfere with the sodium chloride type crystal structure of theantimony-tin. In some cases, the carrier-to-noise ratio will be improvedby as little as 0.6 atomic % of the third element. Somewhat higherconcentrations, e.g. 3 to 35 atomic %, are useful to increase theamorphous to crystalline transition temperature by a more significantamount.

In the embodiments where the third element increases the transitiontemperature, it is preferred that the third element be present in anamount sufficient to increase the transition temperature by at leastabout 3° C. The third element is generally present in a minor amount,and preferably between 3 and 25 atomic percent. The optimum amount willvary depending on the element selected and can be determined by routineexperimentation.

The amount of antimony and tin and their proportions are such that thecrystalline phase of laser recorded marks comprises sodium chloride typecrystals or crystals which have a slightly distorted sodium chloridetype of crystal structure. This is a type of morphology that is wellknown in the art and can be determined by crystallizing a sample of thealloy in question and performing X-ray or electron beam diffractionanalysis. If the X-ray pattern or electron difraction pattern is thesame as or substantially the same as sodium chloride, it is consideredto be a sodium chloride type of crystal structure. The antimony plus tinatomic percent is preferably at least 65%. The ratio of the atomicpercent of the antimony to the atomic percent of the tin in the alloy ispreferably between 1 and 9. Thus, the alloys useful in the invention canbe represented by the formula:

    Sb.sub.x Sn.sub.y E.sub.z

where E is the third element (or mixture of elements); x, y and zrepresent the atomic percent of the elements in the alloy and the ratioof x to y is between about 1 and 9 and z is between 0.6 and 35 atomicpercent.

For the currently preferred third elements, the preferred alloys havethe following compositions (the numbers following the element, representthe atomic percent in the alloys): Sb66Sn28Ga6, Sb58Sn32Ga10,Sb64Sn30Cd6, Sb52Sn39Cd9, Sb50Sn34Cd16, Sb68Sn8Te24, Sb61Sn26Cr13,Sb67Sn29Bi4, Sb63Sn27Nb10, Sb6Sn27Till, Sb62Sn27Sill, (Sb86Sn14)_(x) O₇,(Sb77Sn23 )_(x) O₇, Sb59Sn32Ni9, Sb70Sn26Fe4, Sb66Sn25Mn9 andSb61Sn28Cull.

Optical recording layers can be prepared by conventional thin filmdeposition techniques such as RF (radio frequency) and DC (directcurrent) sputtering from an alloy target using the alloys of theinvention. Enhancement of sputtering processes by applying magneticfields (magnetron sputtering) can also be used. The thickness of thefilms can be from a few tens to a few hundreds of nanometers dependingon compromises among factors such as contrast, sensitivity, productionrate, material cost, ease of control, data rate, etc.

Supports which can be used include plastic plates, such as polyethyleneterephthalate, polymethyl methacrylate, and polycarbonate, a glassplate, paper and metallic plates such as aluminum.

Recording information on the thin film layers made using the alloy ofthis invention is achieved by focusing an information modulated laserbeam on the layer thereby forming a pattern of information on the layerin the form of crystallized areas in an otherwise amorphous layer.

A useful recording material comprises, starting from the outside surfaceof the recording material, an overcoat layer, a thin film opticalrecording layer and a substrate. In response to a drive signal, theintensity of a diode recording beam focused on the recording layer ismodulated in accordance with information to be recorded.

During recording, the recording material is spun at a constant rate,e.g., 1800 rotations per minute (rpm). As a result, a track ofinformation is recorded on the optical recording layer in the form ofselected crystallized areas. As recording continues, the recording spotis caused to scan radially inward across the recording material, therebycausing information to be recorded along a spiral or concentric track.The sizes and spacings of the recorded information marks vary inaccordance with the information content of the recording laser drivesignal, as well as with radial position on the recording material.

During the readback process, the thus recorded information bearingrecording material is spun at the same rate as it was spun during therecording process. The optical path of a readout laser beam is focusedto a playback spot on the recording material by a high numericalaperture lens. The recording material is of the reflective type so thatthe radiation forming the playback slot is reflected back through thehigh numerical aperture lens after interacting with the informationmarks recorded on the optical recording material. A lens directsreflected laser radiation onto a detector which produces an electricalplayback signal in response to temporal variations (contrast) in theirradiance of the reflected laser radiation falling on the detector.

Other types of recording materials are also useful. For example, areflective substrate such as aluminum can be provided with a recordinglayer comprising an alloy of the invention on both sides of thesubstrate. A useful recording material is thus, aluminum coated on bothsides with a smoothing layer, a layer of the phase change alloy of theinvention and a layer of a clear protective overcoat. In a similarembodiment, the alloy is provided on a clear substrate which is thenadhered to both sides of the substrate with an adhesive. In yet anotherembodiment, the alloy as described is provided on a transparentsubstrate to form the recording layer. The optical recording layer isthen adhered to the recording layer of an identical recording materialwith an adhesive layer. The thickness of the adhesive layer provides forthe optical separation of the two recording layers.

In the examples presented below, the samples were tested for amorphousto crystalline transition temperature. The procedure was as follows.Deposited films to be tested were placed on a hot plate in a flowingnitrogen atmosphere. The films were initially amorphous. The temperaturewas raised at a rate of 10 milli Kelvin per second. During this heating,the specular reflectance of the surface of the layer is monitored untilthe entire layer has crystallized and the reflectance has passed amaximum. The data is analyzed and the amorphous to crystallinetransition temperature is taken as the temperature at which the sampleachieved one half of its total reflectance change.

Also in the examples below, alloys are tested for dynamic performance. Astandard &est format was used to measure the dynamic performance values.Specifically, coatings were deposited on clean glass substrates andtested on a dynamic test stand. The recording head used consisted of a780 nm read diode laser and an 830 nm write diode laser utilizing a 0.55numerical aperture lens. Read power was 0.5 mW with high frequencyinjection. Disks were tested at a radius of about 55 mm, a linearvelocity of 10 m/s and a 2.78 MHz 50% duty cycle write frequency.Carrier to noise ratios were measured with an HP 3585A spectrum analyzerusing a 30 KHz resolution bandwidth Carrier level was measured at 2.78MHz. Noise level was measured at 500 MHz above and below the carrierfrequency and averaged. The optimum recording power (dynamicsensitivity) was the power at which a minimum intensity for the secondharmonic of the carrier frequency was observed. The performance valuespresented below are obtainable on any research quality dynamic opticalrecording test facility that has a sufficiently low system noise level.

The following examples are presented to further illustrate the practiceof the invention.

EXAMPLE 1 (a) Preparation of Optical Recording Medium

An alloy target comprising a mixture of Sb and Sn each in amount of 70Tand 30% atomic, respectively, was co sputtered with a third element; Cr,Nb, Bi, Ti, Si or W.

The sp uttering system was pumped to below 1×10⁻⁶ Torr before thechamber was back filled with 3 mTorr of Ar as the sputtering gas. Aninput power of 50 W was used for the 2 inch diameter Sb₀.7 Sn₀.3 alloytarget. The power and deposition time to the third element target werevaried to achieve varying amounts of the third element in the deposited70 nm thick film. The composition of each film was determined from therate of deposition from the individual targets.

The films were deposited on glass microscope slides and 130 mm glassdisk substrates. Next, the sputtering apparatus was returned back tonormal pressure and film was spontaneously cooled to room temperature.

(b) Characterization of Optical Recording Medium

The glass disk substrate samples obtained in the above mentioned step(glass substrate) were dynamically evaluated for writing performance.Optimum recording power (ORP), carrier-to-noise ratio (CNR), carrier(CARR), written (WNOISE) and unwritten noise (UNIOSE), were determinedat 10 m/s linear velocity and 2.78 MHz recording frequency at 50% dutycycle, to obtain a mark length of 1.8 um. Recording and reading wereperformed through the glass substrate.

Reflectivity (RFLv) of the amorphous film at 830 nm was measured with aspectrophotometer from the film side. If the reflectivity of the layeris too low, e.g. below 15%, tracking will be a problem. If too high,e.g. above 70%, the contrast (DLT R) of the written areas could be toolow.

The change in reflectivity (DLT R) between amorphous and crystallinephase of about 1 μm size mark was measured (also from the film side)with 830 nm diode laser and a microscope The DLT R or contrast isimportant in providing good carrier signal.

(c) Conclusions

The data for the samples are presented below in Table 1. In eachinstance, the performance of the antimony-tin alloy was improved by theaddition of a third element. In some instances, the amorphous tocrystalline transition temperature is improved. In other instances, theCNR is improved.

Cr

Improvement in dynamic recording is achieved by addition of Cr to Sb₇₀Sn₃₀ alloy film. Up to 17.4 atomic % of Cr was added with continuousimprovement in CNR, written and unwritten noise, indicating that higherconcentrations of Cr may produce further improvements.

Bi

Addition of Bi at low concentrations, between 0.7 to 4.7 atomic %,produced improvement in CNR, written and unwritten noise. Atconcentrations higher than 5.0 atomic % the sputtering film wascrystalline.

Nb

Addition of Nb, from 0.6 to 15.6 atomic % continuously improves CNR,written and unwritten noise. Nb at concentrations of 9.8 atomic % orhigher, also increases the transition temperature of amorphous phase,improving the thermal stability.

Ti

Ti at concentration of 2.3 atomic % or lower did not produce anyimprovement in writing performance. Concentrations of 3.9 to 6.1 atomic% produced crystalline film. Concentrations of 8.6 atomic % or higherimproved CNR.

Si

Addition of Si at 6.2 atomic % or higher increased the transitiontemperature of the amorphous phase, improving the thermal stability ofthe film.

W

Improvement in written noise and CNR is achieved by addition of tungstenof up to 13.14 atomic %. A tungsten concentration of 9 46 atomic % orhigher, also increases the transition temperature of the amorphousphase, improving the thermal stability.

Pb

Addition of Pb to Sb₇₀ Sn₃₀ at low concentrations (from 1.05 to 7.48atomic %) increases the transition temperature of the amorphous phase upto 135° C., improving thermal stability of the film. Compositions withPb concentration higher than 7.48 atomic % produce crystalline films asmade. Dynamic performance is also improved by addition of lead. Lowerwriting noise produces higher signal to noise ratio, while sensitivityand carrier intensity is essentially unchanged, relatively to thecontrol.

Hf

At hafnium concentrations from 1.29 atomic % to 8.67 atomic %, increasesthe transition temperature of the amorphous phase, improving the thermalstability of the film. Dynamic performance is also improved by additionof hafnium up to 8.67 atomic %. Lower writing noise produces bettersignal to noise ratio. At concentrations of hafnium above 8.67 atomic %,the film becomes too insensitive and contrast (change in reflectancebetween amorphous and crystalline phase) is reduced.

                                      TABLE I                                     __________________________________________________________________________    (Sb.sub.70 Sn.sub.30).sub.100-x E.sub.x                                       E ×                                                                          DYNAMIC PERFORMANCE @ 10 m/s                                                                        DLT R                                                                              RFLv                                                                              T. TMP                                    atomic %                                                                           ORP CNR                                                                              CARR                                                                              WNOISE                                                                              UNOISE                                                                             12/100                                                                             830 nm                                                                            °C.                                __________________________________________________________________________    0.0  4.12                                                                              50.75                                                                            -9.5                                                                              -60.25                                                                              -70.25                                                                             20.5 56.7                                                                              100                                       Cr                                                                            0.9  4.58                                                                              54.50                                                                            -8.8                                                                              -63.30                                                                              -67.55                                                                             18.0 56.0                                                                              72                                        4.0  5.09                                                                              56.20                                                                            -8.9                                                                              -65.10                                                                              -68.30                                                                             18.5 56.5                                                                              74                                        8.3  6.18                                                                              57.40                                                                            -9.8                                                                              -67.20                                                                              -69.65                                                                             18.9 56.7                                                                              78                                        13.0 7.57                                                                              56.80                                                                            -12.0                                                                             -68.80                                                                              -71.10                                                                             14.6 57.3                                                                              82                                        17.4 9.75                                                                              57.40                                                                            -14.4                                                                             -71.50                                                                              -72.20                                                                             10.8 57.6                                                                              91                                        Bi                                                                            0.7  4.43                                                                              56.50                                                                            -9.2                                                                              -65.70                                                                              -75.15                                                                             20.7 54.2                                                                              103                                       4.7  4.46                                                                              56.60                                                                            -9.3                                                                              -65.90                                                                              -75.20                                                                             20.8 54.1                                                                              93                                        6.0  CRYSTALLINE FILM                                                         Nb                                                                            0.6  4.39                                                                              54.35                                                                            -8.9                                                                              -63.25                                                                              -71.50                                                                             18.5 54.0                                                                              81                                        1.3  4.48                                                                              55.90                                                                            -8.8                                                                              -64.70                                                                              -68.20                                                                             16.8 54.3                                                                              77                                        2.7  5.37                                                                              57.80                                                                            -9.4                                                                              -67.20                                                                              -75.05                                                                             12.2 55.1                                                                              77                                        5.4  7.12                                                                              60.40                                                                            -12.3                                                                             -72.70                                                                              -74.80                                                                             11.7 57.7                                                                              88                                        9.8  10.67                                                                             59.75                                                                            -14.2                                                                             -73.95                                                                              -74.50                                                                              2.9 58.3                                                                              113                                       15.6 13.45                                                                             58.25                                                                            -15.4                                                                             -73.65                                                                              -74.50                                                                             --   --  153                                       Ti                                                                            1.1  4.25                                                                              48.35                                                                            -8.8                                                                              -57.15                                                                              -57.45                                                                             21.0 58.0                                                                              60                                        2.3  4.40                                                                              41.60                                                                            -9.1                                                                              -50.70                                                                              -47.80                                                                             19.6 60.1                                                                              55                                        3.9  CRYSTALLINE FILM                                                         6.1  CRYSTALLINE FILM                                                         8.6  6.68                                                                              52.65                                                                            -13.1                                                                             -65.75                                                                              -66.60                                                                             11.9 64.3                                                                              61                                        11.5 8.62                                                                              53.40                                                                            -15.1                                                                             -68.50                                                                              -68.75                                                                             11.9 62.6                                                                              81                                        Si                                                                            1.0  4.16                                                                              44.15                                                                            -9.2                                                                              -53.35                                                                              -57.20                                                                             17.8 64.3                                                                              63                                        1.7  4.16                                                                              43.65                                                                            -8.9                                                                              - 52.55                                                                             -55.75                                                                             19.4 62.3                                                                              72                                        2.7  4.13                                                                              45.80                                                                            -8.8                                                                              -54.60                                                                              -57.55                                                                             22.2 61.7                                                                              77                                        4.3  4.21                                                                              48.35                                                                            -8.8                                                                              -57.15                                                                              -59.65                                                                             24.3 62.2                                                                              88                                        6.2  4.49                                                                              48.40                                                                            -8.9                                                                              -57.30                                                                              -59.70                                                                             23.2 60.5                                                                              104                                       8.5  4.80                                                                              47.75                                                                            -8.9                                                                              -56.65                                                                              -59.15                                                                             23.9 57.8                                                                              112                                       11.1 5.88                                                                              47.90                                                                            -13.1                                                                             -61.00                                                                              -63.50                                                                             21.5 54.9                                                                              132                                        1.09                                                                              4.34                                                                              52.10                                                                            -9.4                                                                              -61.50                                                                              -73.00                                                                             21.7 56.3                                                                              90                                         3.33                                                                              4.88                                                                              58.10                                                                            -9.5                                                                              -67.60                                                                              -73.00                                                                             21.1 56.4                                                                              91                                         6.16                                                                              6.61                                                                              61.00                                                                            -11.2                                                                             -72.20                                                                              -73.50                                                                             17.9 57.8                                                                              104                                        9.46                                                                              11.22                                                                             60.90                                                                            -12.2                                                                             -73.10                                                                              -74.00                                                                             12.1 58.8                                                                              135                                       13.14                                                                              13.23                                                                             59.20                                                                            -13.6                                                                             -72.80                                                                              -74.00                                                                              6.6 58.4                                                                              174                                       17.24                                                                              13.94                                                                             50.80                                                                            -15.5                                                                             -66.30                                                                              -69.00                                                                              6.9 58.1                                                                              183                                       Pb                                                                             1.05                                                                              4.64                                                                              56.30                                                                            -9.5                                                                              -65.80                                                                              -73.90                                                                             15.7 61.2                                                                              134                                        7.48                                                                              4.97                                                                              58.20                                                                            -9.4                                                                              -67.60                                                                              -72.90                                                                             18.2 59.9                                                                              135                                       19.27                                                                              CRYSTALLINE FILM                                                         31.94                                                                              CRYSTALLINE FILM                                                         Hf                                                                             0.02                                                                              4.46                                                                              49.90                                                                            -9.3                                                                              -59.20                                                                              -70.55                                                                             16.5 62.7                                                                              72                                         0.05                                                                              4.47                                                                              49.70                                                                            -9.6                                                                              -59.30                                                                              -70.55                                                                             18.2 61.8                                                                              73                                         1.29                                                                              4.53                                                                              54.00                                                                            -9.1                                                                              -63.10                                                                              -71.40                                                                             16.9 62.4                                                                              82                                         4.39                                                                              6.03                                                                              58.90                                                                            -10.3                                                                             -69.20                                                                              -72.60                                                                             17.2 63.1                                                                              98                                         8.67                                                                              8.95                                                                              57.30                                                                            -14.1                                                                             -71.40                                                                              -72.65                                                                             11.4 64.0                                                                              128                                       12.73                                                                              LOW CONTRAST AND SENSITIVITY                                                                         8.1 63.7                                                                              150                                       14.83                                                                              LOW CONTRACT AND SENSITIVITY                                                                         4.7 63.9                                                                              150                                       __________________________________________________________________________     DLT R = Change in reflectance with exposure to 12 mW and 100 ns laser         pulse, measured with static pit tester on the film surface.                   RFLv = Reflectivity of the unrecorded amorphous film at 830 nm, measured      with BECKMAN MODEL DKA Spectrophotometer, film surface.                       T. TMP = Transition temperature, (amorphous film to crystalline).        

EXAMPLE 2

In a separate series of examples, samples were prepared in a similarmanner except that the alloys were sputtered from a mixed power targetinstead off cosputtering from two targets. These samples were tested fortransition temperature as described previously and were tested forwriting sensitivity and contrast on a static pit tester. The static pittester provides automated facilities in which a microcomputer controlsthe sample position, the laser power and the laser pulse width. Eachrecording layer is exposed with a 790 nm laser diode in the static pittester to produce a matrix of spots in which the laser power is variedfrom 0.7 to 12 mW and the pulse width varied from 50 to 30,000nanoseconds. The suitability of the recording layer for opticalrecording is determined by measuring the change in reflection betweenthe exposed and the unexposed areas of the sample, i.e. between thecrystalline and the amorphous states.

In the table, the laser lower needed to write at a 50 nanosecond pulsewidth is a measure of the sensitivity of the film. A lower powerindicates a higher sensitivity.

In addition, the ratio of antimony to tin was varied. The results areshown in Table 2.

                                      TABLE II                                    __________________________________________________________________________    Sbx Sny + Ez Alloy                                                            for Write-Once Optical Recording                                                                    Power needed                                                                          ΔR at                                                    Transition                                                                           to write at                                                                           100 ns                                          E    Composition                                                                             Temp. (°C.)                                                                   50 ns. (mW)                                                                           12 mW (%)                                       __________________________________________________________________________    Control                                                                            Sb70Sn30  100    4       14                                              Ga   Sb75Sn22Ga3                                                                             130    3       12                                              Ga   Sb66Sn28Ga6                                                                             158    4       15                                              Ga   Sb58Sn32Ga10                                                                            161    4       15                                              Ga   Sb60Sn22Ga18                                                                            210    5        8                                              Cd   Sb53Sn43Cd4                                                                             122    2.5     22                                              Cd   Sb64Sn30Cd6                                                                             150    2.5     23                                              Cd   Sb77Sn17Cd6                                                                             167    3       21                                              Cd   Sb52Sn39Cd9                                                                             140    2.5     21                                              Cd   Sb73Sn15Cd12                                                                            177    3       22                                              Cd   Sb44Sn44Cd12                                                                            125    2.5     17                                              Cd   Sb50Sn34Cd16                                                                            155    3       15                                              Cd   Sb62Sn21Cd17                                                                            188    4       17                                              Te   Sb68Sn8Te24                                                                             125    10      13                                              Ni   Sb59Sn32Ni9                                                                             109    12       7                                              Fe   Sb70Sn26Fe4                                                                             110    5       15                                              Mn   Sb66Sn25Mn9                                                                             136    4       15                                              Cu   Sb61Sn28Cu11                                                                            123    4       13                                               O*  (Sb86Sn14) × Oy                                                                   150    2.5     12                                              O    (Sb82Sn18) × Oy                                                                   160    3       11                                              O    (Sb77Sn23) × Oy                                                                   170    2.5     12                                              O    (Sb68Sn32) × Oy                                                                   130    3       13                                              __________________________________________________________________________     *Films were prepared by reactive sputtering. 1.3% of O.sub.2 in Ar was        used during sputtering. Total pressure was 8 mtorr. Flow rate was 23 cpm.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

We claim:
 1. A method of recording information comprising the stepof:(a) providing a recording material comprising a write-once amorphousthin-film optical recording layer of an alloy, said alloy comprising (i)antimony and tin in a proportion such that crystalline laser recordingmarks of said alloy have a sodium chloride type crystal and (ii) atleast one other element selected from the group consisting of cadmium,gallium, titanium, silicon, manganese, tellurium, niobium, iron, copper,tungsten, molybdenum, sulfur, nickel, oxygen, selenium, thallium,arsenic, phosphorous, gold, palladium, platinum, hafnium and vanadium,and (b) focusing an information modulated laser beam on said recordinglayer to form a pattern of crystalline and amorphous areas in the layer;wherein all of said crystalline areas are in the same crystalline statewith a reflectivity that is different from the amorphous areas.
 2. Arecording method according to claim 1 wherein the recording materialwherein the other element is selected from the group consisting ofcadmium, gallium, nickel, iron, manganese, copper, oxygen, niobium,tellurium and silicon, and is present in an amount sufficient toincrease the amorphous to crystalline transition temperature of saidalloy.
 3. A recording method according to claim 2 wherein the otherselected element is present in an amount sufficient to increase theamorphous to crystalline transition temperature by at least about 3° C.4. A recording method according to claim 3 wherein the selected elementis present in an amount between 3 and 35 atomic percent.
 5. A recordingmethod according to claim 1 wherein the other selected element isselected from the group consisting of chromium, bismuth, niobium andtungsten and is present in an amount sufficient to improve the carriernoise ratio when said material is used for optical recording.
 6. Arecording method according to claim 1 wherein said alloy is representedby the formula:

    Sb.sub.x Sn.sub.y E.sub.z

where E is the third element and is selected from the group consistingof cadmium, titanium, silicon, manganese, tellurium, niobium, iron,copper, tungsten, molybdenum, nickel, oxygen, thallium, arsenic,phosphorous, gold, palladium, platinum, hafnium and vanadium; x, y and zrepresent the atomic percent of the elements in the alloy and the ratioof x to y is between about 1 and 9 and z is between 0.6 and 35 atomicpercent.
 7. A recording method according to claim 1 wherein said alloyis an alloy selected from the group consisting of Sb₆₆ Sn₂₈ Ga₆, Sb₅₈Sn₃₂ Ga₁₀, Sb₆₄ Sn₃₀ Cd₆, Sb₅₂ Sn₃₉ Cd₉, Sb₅₀ Sn₃₄ Cd₁₆, Sb₆₈ Sn₈ Te₂₄,Sb₆₁ Sn₂₆ Cr₁₃, Sb₆₇ Sn₂₉ Bi₄, Sb₆₃ Sn₂₇ Nb₁₀, Sb₆₂ Sn₂₇ Ti₁₁, Sb₆₂ Sn₂₇Si₁₁, (Sb₈₆ Sn₁₄)_(x) O_(y), (Sb₇₇ Sn₂₃)_(x) O_(y), Sb₅₉ Sn₃₂ Ni₉, Sb₇₀Sn₂₆ Fe₄, Sb₆₆ Sn₂₅ Mn₉ and Sb₆₁ Sn₂₈ Cu₁₁.